The corpus callosum, which connects the two cerebral hemispheres, is the largest fiber tract in the human brain. This fiber tract is severed in patients who undergo complete callosotomy, resulting in a disconnection of the hemispheres at the cortical level. Lateralized testing of these patients can reveal dramatic hemispheric differences in perceptual and cognitive processing, yet paradoxically, their behavior often appears fully integrated. The purpose of this proposal is to investigate the role of the corpus callosum and non-callosal mechanisms in interhemispheric integration. It has been suggested that intrahemispheric processing is more efficient than interhemispheric processing and therefore processing will tend to occur within one hemisphere when task demands are low. As task demands increase, however, research has demonstrated that the other hemisphere is increasingly recruited, requiring integration of information and resources between the two hemispheres. To determine the role of the corpus callosum in interhemispheric integration, we plan to continue behavioral testing of complete callosotomy patients. In addition, we are expanding our patient population to include those with partial lesions of the corpus callosum in order to characterize the role of callosal subregions in interhemispheric integration. Proposed experiments also incorporate new methodologies, specifically, diffusion tensor imaging, functional neuroimaging and electrophysiological recording of neural activity. Our research proposal centers on four specific aims. The first aim is to investigate the role of specific callosal regions in the binding of visual features into unified object representations. The second aim is to explore the effect of hemispheric specialization and task difficulty on the deployment of processing resources. The third aim is to investigate the effect of hemispheric differences in spatial representation on the integration of perception and movement between the two hemispheres. The fourth aim explores the extent to which the disconnected hemispheres are able to monitor and respond to processing events in the other hemisphere. Taken together, this research will provide important insights into the specialized roles of the two hemispheres and the ways in which they interact via the corpus callosum and non-callosal mechanisms [unreadable] [unreadable]